617
07
06
Ic
romagnetic exchange between chains. Work is presently underway to model the magnetic data via equations developed for Ising linear chains4 and to relate the exchange phenomena to the observed low temperature optical spectra.
I
\
References and Notes
.
(1) R. L. Carlin. Acc. Chem. Res., 9, 67 (1976), and references therein. (2) R. J. Doedens, Prog. lnorg. Chem., 21, 209 (1976), and references therein. (3) A. P. Ginsberg, Inorg. Chim. Acta Rev., 5, 45 (1971), and references therein. (4) D. B. Losee, J. N. McElearney, G. E. Shankle, R. N. Carlin, D. J. Cresswell, and W. T. Robinson, Phys. Rev. 6, 6, 2185 (1973). (5) R. D. Spence and A. C. Botterman. Phys. Rev. 6, 9, 2993 (1975). (6) S . Foner. R. B. Frankel, W. M. Reiff, B. F. Little, and G. J. Long, Solid State Commun., 16, 159 (1975). (7) E. R. Jones, Jr., and J. A. Stone, J. Chem. Phys., 56, 1343 (1972). (8)It is interesting to note that this stoichiometry is consistent with the first report of a product formed between Co2+ and the hippurate ion (H. Schwartz, Ann.. 54, 29 (1845)) but not with the recently reported hexahydrate (G.Marcotrigiano and G. C. Peliacani. lnorg. Nucl. Chem. Lett., 11, 643 (1975)). (9) The conventional reliability index R = w',kF,I Fc wI F,I is cited. Scattering factors for carbon, nitrogen, oxygen, and cobalt are taken from the paper by D. Cromer and J. Waber, Acta Crystallogr., 18, 104 (1965), while that for hydrogen is from "International Tables for X-Ray Crystallography", Vol. Ill, Kynoch Press, Birmingham, England, 1968. (10) J. N. Brown, H. R. Eichelberger, E. Schaeffer, M. L. Good, and L. M. Trefonas, J. Am. Chem. Soc., 93, 6290 (1971). (11) J. N. Brown and L. M. Trefonas, Inorg. Chem., 12, 1730 (1973).
-1
-1
1 0
2
6
4
8
IO
1 , *K
Figure 3: Specific magnetization vs. temperature for several values o f applied magnetic field for a powdered sample o f Co[(C(,H5)C O N H C H ? C 0 0 ] 2 4 H 2 0 . (Right hand ordinate is for the curves at I O kOe and 5000 Oe. Left hand ordinate i s for the turves at 250,500. 1000, and 1500 Oe.)
;/x
Helen Eichelberger, Richard Majeste Rene Surgi, Louis Trefonas,* Mary L. Good* Department of Chemistry, Unicersity of New Orleans Lakefront, New Orleans, Louisiana 70122 David Karraker' Chemistry Dioision, Sacannah Ricer Laboratory E . 1. duPont de Nemours and Co. Aiken, South Carolina 29801 Receiced September I O , 1976
the bridge. The chains show no close contact distances to each other with the closest cobalt-cobalt contact distance across two chains, of 6.90 A along t h e y cell axis. The hippurate molecules are bonded to the cobalt through Reductive Coupling of Adjacent Ligands in a the carboxyl oxygen atoms as has been previously observed in Seven-Coordinate Molybdenum(I1) Isocyanide Complex' the case of the copper hippurate.l0-" Figure 2 shows how these Sir: molecules fan out from the backbone like alternating rungs of a ladder. The two remaining water molecules in the structure Recently we have synthesized and structurally characterized lie between the hippurate steps and have no close contact with the seven-coordinate molybdenum(I1) complexes [MoL7I2+ the cobalt ions. and [MOL6X]+, where L is tert-butyl isocyanide and X = CI, Zero field magnetic susceptibility data for the powdered Br, The structures consist of a capped trigonal prism with complex were obtained from 2.5 to 80 K. The plot of 1/XM vs. either halide or isocyanide as the capping ligand (Figure 1). T (not shown) was indicative of Curie-Weiss law behavior The short nonbonded contacts between coordinated carbon above 40 K (with 0 = 32' and C = 0.46). Between 40 and 10 atoms suggested that ligand migration or coupling reactions, K a broad minimum, typical of an antiferromagnet, was obknown to occur for other metal isocyanide c ~ m p l e x e s , might ~-~ served, followed by a sharp, essentially linear decrease in l / x v be especially facile for these heptacoordinate molybdenum(I1) a s the temperature was lowered below 10 K. Susceptibility cations. behavior of this type is expected for a metamagnet. However, A suspension containing 3 mmol of red-orange [(Rthe metamagnetic character of the compound is more conN C ) ~ M O I ] I R, ~ = tert-butyl, and 10 mmol of zinc dust in vincingly exhibited by the temperature dependent magnetitetrahydrofuran was allowed to reflux under nitrogen for 2 h. zation data taken with magnetic fields in the range of 0-10 The final, deep red solution was filtered and the solvent rekOe. Field dependent isothermal magnetization curves (not moved in vacuo. Red, air-stable crystals were obtained in 90% shown) were obtained from 2.59 to 5.62 K in fields up to 10 yield upon recrystallization from acetone or benezene and kOe. Below 3.14 K S-shaped curves characteristic of metadiethyl ether. Analytical data were consistent with the emmagnets were observed. Curves of specific magnetization vs. pirical formula ( R N C ) ~ M O I ~ HThe ~ . ~infrared O spectrum of T a t constant applied fields are shown in Figure 3. Note that the compound mulled in carbon tetrachloride had absorptions the specific magnetization maximum shifts to lower tempera t 2128 cm-' (br, mult), assigned to terminal isocyanide atures as the external field strength is increased, again indistretching modes, bands a t 1593 and -1400 cm-' in the C=C cating that the complex exhibits metamagnet behavior rather and C=N stretching region, two N-H stretching frequencies than a "spin-flop" transition. At an applied field of approxiat 3102 and 3160 cm-I, and an N-H deformation band a t mately 1500 Oe, the antiferromagnetic transition disappears 15 13 cm-l. The assignment of the N-H stretching bands was and ferromagnetic saturation is observed. These magnetic data verified by a deuterium exchange experiment. They shifted to are analogous to those reported for the Co(pyr)zCI? ~ y s t e m ~ - ~2309 and 2359 cm-I, respectively, when the complex was which has been interpreted in terms of strong ferromagnetic deuterated by shaking a solution of it in chloroform with DzO exchange interactions along the chains and weak antiferfor 1 h, separating the layers, and precipitating the product Communications to the Editor
618
[It-But(cl~t-BunnCIZYoll'
Figure 1. Molecular geometry o f the cations in (left) [(r-C4HgYCh,Mol]l,J the starting material, and (right) [(r-C4HgNC)4 ( r C4HgHN,C,C,NHC4H9-r)Mol] I, the product, as determined by x-ray diffraction. interatomic distances (in standard deviations o f 0.03 or less.
A
A) shown
have estimated
with ether. The N-H deformation similarly shifted to a lower frequency upon deuteration. The 100-MHz proton N M R spectrum of the compound in CDC13 showed methyl resonances of the tert-butyl groups a t 6 1.48 and 1.66 ppm of relative intensities 2:l. A small peak a t 9.68 ppm with an integrated intensity about one-thirtieth that of the combined tert-butyl resonances provided further confirmation of the empirical formula. This resonance did not appear when the complex was dissolved in acetone-d6 containing a few drops of DzO. Pulsed Fourier-transform I3C N M R spectra also revealed two tert-butyl environments, with methyl carbon resonances at 29.96 and 30.28 ppm and tertiary carbon shifts of 56.89 and 54.75 ppm, relative intensities 2:1, respectively. The resonances of the carbon atoms of the tert-butyl isocyanide ligands bonded to molybdenum appeared a t 157.1 ppm, and the chemical shift of the corresponding carbon atoms of the (LH)2 ligand was 192.9 ppm. An x-ray crystallographic study was required to establish the true nature of the product. Using 4038 observed reflections collected with M o K a radiation (28 I 55"), the structure was solved by heavy atom methods and refined to a current value of 0.059 for R I ,the conventional agreement factor." As shown in Figure 1, the molecular geometry is very similar to that of the starting [(RNC)6MoI]+ cation with one major difference. In the product there is a bond between the two carbon atoms on the edge opposite the capped face. The resulting C-C (1.38 f 0.02 A) and C-N (1.33 f 0.02 A) distances in the coupled ligand require multiple bond character, and the mean C-N-C angle of 128' is consistent with the presence of N - H bonds. There has not yet been any attempt to locate hydrogen atoms in the difference Fourier maps. The structural and spectroscopic results indicate that the product of the reductive coupling reaction may be considered as a bis(alky1amino)acetylene derivative with substantial bond delocalization, RHN,C,C--NHR.l2 Although the free ligand does not appear to be a known compound,I4 its stability is enhanced by coordination to the molybdenum atom. Regarding the ligand as an acetylene molecule would result in a 16-electron molybdenum(I1) cation for which there is some precedence.' Alternatively, the complex achieves a closed shell configuration if the ligand is viewed as a dicarbene. These two extremes and one of several possible charged resonance forms are depicted below. We may view the present reaction formally
RHN
c'
111
/c RHN
- Mo
RHN
\
c\
I p M o
/c RHN
-
RHI~
\-
c\
I,Mo
/!-
RHN
+
as the addition of one electron and one proton to each of two Journal of the American Chemical Society
isocyanide ligands which then couple to one another on the unique edge. Such a process would be similar to carbene formation by addition of H-X across the C r N triple bond of a coordinated isocyanide ligand.16 Here the group X is an adjacent carbon atom in the coordination sphere. Although we emphasize that the mechanism in which two isocyanide ligands are reductively coupled is presently unknown, the reaction may be an example of a higher coordination effect. The close nonbonded contact between the ligands in [(RNC)6MoI]+ might enhance the propensity for carboncarbon bond formation. Molecular orbital calculation^'^ of d4 capped trigonal prismatic compounds such as [ (RNC)6MoI]+ show a small positive overlap population between the two ligands on the unique edge of the coordination polyhedron. Further work is in progress to test this and other mechanistic possibilities. Acknowledgments. This work was supported by Grant No. MPS75-05243 from the National Science Foundation. We thank Professor R. Hoffmann for a preprint of ref 17 and the Camille and Henry Dreyfus Foundation for a Teacher-Scholar Grant applied to the purchase of the computer-controlled diffractometer. References and Notes (1) Part 6 of a continuing series on higher coordinate cyanide and isocyanide complexes. For Part 5, see ref 2. (2) D. L. Lewis and S. J. Lippard, J. Am. Chem. SOC., 97, 2697 (1975). (3) (a) M. Novotny and S. J. Lippard, J. Chem. Soc., Chem. Commun., 202 (1973); (b) C. T. Lam, M. Novotny, D. L. Lewis, and S. J. Lippard, to be submitted for publication. (4) D. F. Lewis and S. J. Lippard, Inorg. Chem., 11, 621 (1972). (5) For a review, see S. J. Lippard, Prog. Inorg. Chem., 21, 91 (1976). (6) (a) Y. Yamamoto and H. Yamazaki, Coord. Chem. Rev., 8,225 (1972); (b) K.Aoki and Y. Yamamoto, horg. Chem., 15,48 (1976) and references cited therein. (7) S. Otsuka, A. Nakamura, T. Yoshida, M. Naruto, and K. Ataka, J. Am. Chem SOC.,95, 3180 (1973). (8) E. Crociani and R. L. Richards, J. Chem. Soc., Chem. Commun., 127 (1973). (9) P. M. Treichel, Adv. Organomet. Chem., 11, 21 (1973). (IO) Calcd for C30H56N612MO: C, 42.36; H, 6.64; N, 9.88; I, 29.84. Found (two preparations): C, 42.16, 42.64; H, 6.68, 6.27; N, 9.80, 9.83; I, 29.97, 29.91. (1 1) Crystallographic data: C3,&&12MO; M = 850.6, orthwhombic; a = 21.995 (3), b = 19.849 (3), c = 18.536 (3) A; V = 8092 A3; Z = 8,p ab = 1.396 pabsd = 1.395 (2)g/cm3; spacegroup Pbca;R, = 8 11 Fol - p F l l / Z I F , I , for fo2 t 3u(f0*). (12) Recent studies of reactions of bis(dialkylamino)alkynes with metal carbonyls demonstrated cleavage of the triple bond with attendant formation of bridging dialkylimmoniocarbene ligands.13 (13) (a) R. B. King and C. A. Harmon, Inorg. Chem., 15, 879 (1976); (b) R. C. Pettersen and G. G. Cash, Abstr. Am. Cryst. Assoc., 4, 64 (1976). (14) H. G. Viehe, "Chemistry of Acetylenes", Marcel Dekker, New York, N.Y., 1969.. D O 861-912. (15) J. A. Segal, M. L. H. Green, J. C. Daran, and K. Prout, J. Chem Soc., Chem. Commun.. 766 11976). (16) (a) D. J. Cardin. E. Cetinkaya, M. J. Doyle, and M.F. Lappert. Chem. SOC. Rev., 2,99 (1973); (b) F. A. Cotton and C. M. Lukehart, Prog. horg. Chem., 16, 487 (1972). and references cited therein. (17) R. Hoffmann, B. F. Beier, E. L. Muetterties, and A. R. Rossi. submitted for publication. 7r
C. T. Lam, P. W. R. Corfield, S. J. Lippard* Department of Chemistry, Columbia University New York, New York 10027 Received September 13, 1976 The Structure of Juncusol. A Novel Cytotoxic Dihydrophenanthrene from the Estuarine Marsh Plant
Juncus roemerianus' Sir: The Mississippi salt marsh is an irregularly flooded estuary dominated by the needlerush Juncus roemerianus (Juncaceae). Studies by de la Cruz2 on the ecology of Mississippi salt marsh on the primary production and decomposition of marsh plants have served to focus attention on their value to estuarine animals including those of commercial importance. W e therefore have initiated a continuing chemoecological study
/ 99:2 / January 19,1977
